title: Cs2.91Na1.34Fe(3+)0.25[Fe3O(SO4)6(H2O)3]·5H2O, a member of the Maus's salt family.
abstract: The title compound, tricaesium sodium iron(III) μ3-oxido-hexa-μ2-sulfato-tris[aquairon(III)] pentahydrate, Cs2.91Na1.34Fe(3+)0.25[Fe3O(SO4)6(H2O)3]·5H2O, belongs to the family of Maus's salts, K5[Fe3O(SO4)6(H2O)3]·6H2O, which is based on the triaqua-μ3-oxido-hexa-μ-sulfato-triferrate(III) anion, [Fe3O(SO4)6(H2O)3](5-), with Fe in a characteristically distorted octahedral coordination environment, sharing a common corner via an oxide O atom. Cs in four different cation sites, Na in three different cation sites and five water molecules link the anions in three dimensions and set up a crystal structure in which those parts parallel to (001) and within 0.05 < z < 0.95 have a distinct trigonal pseudosymmetry, whereas the cation arrangement and bonding near z ∼ 0 generate a clear-cut noncentrosymmetric polar edifice with the monoclinic space group C2. The structure shows some cation disorder in the region near z ∼ 1/2 where one Na atom in octahedral coordination is partly substituted by Fe(3+), and a Cs atom is substituted by small amounts of Na on a separate nearby site. One Na atom, located on a twofold axis at z = 0 and tetrahedrally coordinated by four sulfate O atoms of two [Fe3O(SO4)6(H2O)3](5-) units, plays a key role in generating the noncentrosymmetric structure. Three of the seven different cation sites are on twofold axes (one Na(+) site and two Cs(+) sites), and all other atoms of the structure are in general positions.
authors.affiliation: Institute of Chemical Technology and Analytics, Vienna University of Technology, Getreidemarkt 9/164SC, A-1060 Vienna, Austria.
authors.forename: Kurt
authors.initials: K
authors.lastname: Mereiter
keywords: Maus's salt family; crystal structure; inorganics